Applying textures to your photographs can create a different look and feel. This can be very subtle to a complete change in the look and feel of an image. Layering works particularly well with portraiture when the maker wishes to convey an old or sandy (grainy) kind of feel. In this example, I applied a photograph of sandstone ontop of a photograph of an Italian town (Monorola). In addition I punched up the colours.
It obviously isn't anything remotely to what I saw with the naked eye. However, since it was raining, evening shot (quite dark) and generally drab, why wouldn't I want to alter it? Who would really want to see the original capture? Not me :)
Experiment with textures. Shoot some photographs of sand, various stones (granite and marble work particularly well), old wood etc. Then copy it as a new layer into photoshop (or our editor of choice), reduce the opacity and see what happens. If you are lazy, just download textures from the various free sites and give it a go.